Use _.

Author: kazutakahirata

llvm/lib/Support/CommandLine.cpp

@@ -602,7 +602,7 @@ static Option *LookupNearestOption(StringRef Arg,
   // Find the closest match.
   Option *Best = nullptr;
   unsigned BestDistance = 0;
-  for (const auto &[Key, O] : OptionsMap) {
+  for (const auto &[_, O] : OptionsMap) {
     // Do not suggest really hidden options (not shown in any help).
     if (O->getOptionHiddenFlag() == ReallyHidden)
       continue;